Erasure detection of transmon dual-rail qubit with symmetrically coupled readout (Part 1/2)

Erasure qubits have been proposed as a platform for implementing hardware-efficient quantum error correction. These are qubits for which nearly all errors are detectable “erasure” errors, and which therefore can facilitate QEC with favorable thresholds. A key requirement to utilize them, however, is the ability to perform a measurement that can flag an erasure without disturbing the qubit in cases when it wasn’t erased. In this two-part talk, we will discuss erasure detection in a dual-rail erasure qubit based on tunable transmons, where the main source of error - amplitude damping - is converted to erasure. We focus on a protocol for erasure detection using a single readout resonator which is symmetrically coupled to both transmons in the dual-rail qubit. This approach enables fast erasure detection with simple and compact circuit components, minimizing footprint overhead compared to standard transmon architectures.

In part I, we will discuss theoretically the symmetrically-coupled readout cavity proposal, and in particular, the condition for chi-matching and other design requirements. In part II, we will present experimental result demonstrating the ability to perform fast erasure detection with minimal induced dephasing on the logical qubit.